Toothbrushes generally comprise a head and a grip handle arranged to define a toothbrush longitudinal direction (not necessarily a straight line) between them, with a neck region longitudinally between the grip handle and the head. Typically toothbrush handles and heads are made of a hard plastic material such as polypropylene. Tooth-cleaning elements such as bristles, e.g. typically filaments made from nylon, are mounted in the head and project in a transverse direction relative to this longitudinal direction from the head.
It is known to provide toothbrushes with a resiliently flexible region in their structure to absorb excessive brushing pressures during use and thereby reduce the likelihood of damage to teeth and soft oral tissues such as gums resulting from such excessive pressure. U.S. Pat. No. 5,054,154 discloses a toothbrush with an elastic segment between its handle and its head, in the form of widthways cut-outs across the toothbrush containing an elastic rubbery material. Another known form of such a flexible region is that disclosed in EP-A-0 336 641A being in the form of an S-bend undulating region longitudinally between the head and the handle, comprising limbs extending in the transverse direction and integrally linked by folds with troughs between the limbs, and preferably made more rigid by means of a longitudinal rib through the folds. A modification of such a region of limbs and folds is disclosed in WO-A-01/43580 in which there is a thermoplastic elastomer material in the folds between the limbs, and in which the flexibility can be controlled by a longitudinally moveable slider which intersects the limbs.
Since these early publications toothbrushes have been sold by the present applicant under the trademarks AQUAFRESH™ and DrBEST™ incorporating such an undulating region and attempting to optimize flexibility. The solution adopted in such commercial embodiments has always been the incorporation of a longitudinal rib as described in EP-A-0 336 641. Such toothbrushes have also been sold incorporating additionally a flexible link between the toothbrush head and the neck region of the toothbrush, or located in the neck region of the toothbrush itself. Such toothbrushes are for example disclosed in WO-A-98/37788.
The incorporation of elastomer material parts into toothbrush heads and handles to modify flexibility and for other purposes is also known. For example WO-A-96/28993 discloses an S-bend undulating region longitudinally penetrated by an elastomer material core. WO-A-97/25899 discloses elastomer segments in the toothbrush head to modify flexibility and in the handle to enhance grip and for aesthetic purposes. WO-A-98/05241 discloses elastomer-filled grooves in a toothbrush head to modify flexibility. EP-A-1350442 discloses a toothbrush head made flexible by means of an elastomer-containing hinge. US-D-450928 S discloses a toothbrush handle with an S-bend undulating region in which the troughs of the S-bend undulating region contain an elastomer material, but for an undisclosed technical purpose.
A problem has been encountered with toothbrushes incorporating such an undulating region, especially such toothbrushes which also include the above-mentioned flexible link between the toothbrush head and the neck region of the toothbrush. The problem is that with the prior undulating region incorporating the longitudinal rib the stress experienced by the toothbrush during tooth brushing is not optimally distributed and the toothbrush is prone to breakage during use. In toothbrushes which also include a flexible link between the toothbrush head and the neck region of the toothbrush it has been found that undulating regions of limbs and folds can be so rigid that the flexible link between the toothbrush head and the neck region can be subject to excessive stress during use, resulting in breakage and shortening of useful life. It is an object of the present invention to address these problems. Other objects and advantages of the present invention will be apparent from the following description.